Background and Aim: Inflammatory bowel diseases (IBD) commonly affect women during the reproductive years. The aim of the present study was to evaluate the reproductive histories of patients with ulcerative colitis (UC) and Crohn's disease (CD) considering pregnancies occurring before and after the diagnosis. Method: Case-control study evaluating IBD patients, interviewed by questionnaire about outcome of pregnancy and course of disease. Results: A total of 502 pregnancies from 199 patients in the prediagnosis group and 121 pregnancies from 90 patients in the post-diagnosis group were respectively compared with 996 and 204 pregnancies recorded in a control population. In prediagnosis pregnancies, CD was associated with increased risk of preterm delivery (odds ratio [OR] 4.62, 95% confidence interval [CI] 2.77-7.73; P < 0.001 vs controls and OR 3.52, 95% CI 1.75-7.07; P < 0.001 vs UC) and lower birthweight (P < 0.001 vs UC and controls). In post-diagnosis pregnancies, the rate of live births was lower, but not statistically significant in IBD (OR 0.22, 95% CI 0.04-1.25; P = 0.08) and the birthweight was significantly lower in CD than in UC (P < 0.03) and in controls (P < 0.02). In post-diagnosis pregnancies, a higher incidence of congenital abnormalities was found in IBD patients (5.5% vs 0.0%). The spontaneous abortion rate and therapeutic abortions were significantly higher in post than in prediagnosis pregnancies. Neither disease activity at conception nor treatment appeared to influence the outcome of pregnancy. Conclusions: CD in the preclinical phase has some influence on pregnancy. In patients with IBD our data suggest that conception should not be discouraged. However, because of a modest increase in mild congenital abnormalities and abortions rates, pregnancy in IBD patients should be closely monitored.